Display Pack and Packaging Method and Apparatus

ABSTRACT

A display pack for a consumer product is made of two sheets of corrugated cardboard and a clear plastic container with a flat insertion portion sandwiched between the cardboard sheets. The two cardboard sheets are adhered together in a peripheral area of the package by a heat sensitive adhesive, and the corrugations of the cardboard sheets are crushed and flattened in the peripheral area. To seal the package, the peripheral area of the two cardboard sheets is subject to sufficient pressure to crush the corrugations inside the cardboard sheets and flatten them in that area. Heat is applied to the outer side of the cardboard sheets in the peripheral area and conducted to the adhesive material between the two sheets to activate the adhesive material. A sealer machine with a heated sealing press or parallel sets of heated rollers may be used to carry out the sealing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/374,769, entitled DISPLAY PACK AND PACKAGING METHOD AND APPARATUS,filed Mar. 14, 2006, which claims priority to and the benefit of U.S.provisional application No. 60/711,024, filed Aug. 24, 2005, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to product packaging, and in particular, itrelates to packaging for products suitable for store merchandising.

DESCRIPTION OF THE RELATED ART

A first type of conventional packaging for consumer products, shown inFIGS. 6( a) and 6(b) (which is a cross-sectional view along thedirection of arrows 2-2), is made of two sheets of corrugated cardboard101 and 102, and a clear plastic container 103 having a flat insertionportion 103 a and a chamber portion 103 b. The insertion portion issandwiched between the two cardboard sheets 101 and 102, and the chamberportion 103 b protrudes from the plane of the cardboard sheets via a cut(opening) on one cardboard sheet 101 and is used to hold the productinside. A second plastic container 103′ may be provided and protrudesfrom the other cardboard sheet 102 to form a continuous space for holdthe product. The two cardboard sheets 101 and 102 are adhered togetheraround the periphery with an adhesive 104. A commonly used adhesive is ahot melt glue. The front and back sides of the package are typicallyprinted with product information and other information. (In thesedrawings, the spaces between the various layers are exaggerated toillustrate the relationship among the various layers.) One disadvantageof this type of conventional packaging is that the hot melt glue istypically applied by hand, and thus the seal quality is often difficultto control due to, for example, the varying drying speed of the glue,the placement of the glue, etc. Another disadvantage is that thecorrugation of the cardboard is visible at some of the side edges of thefinished packaging (see FIG. 6( c), a view of the bottom edge of thepackaging of FIG. 6( a)), making the packaging aestheticallyunappealing.

A second type of conventional packaging, shown in FIG. 7( a), is similarto the first type shown in FIGS. 6( a)-(c), but uses one sheet ofcorrugated cardboard 112 (typically the back sheet) and one flat sheetof paper 111 (typically the front sheet, i.e., on the side of theproduct chamber). Sometimes two flat sheets of paper 111 and 111′ areused, one on each side of the corrugated cardboard (see FIG. 7( b). Thecardboard sheet 112 and the flat paper sheet 111 are adhered together bya heat-sensitive adhesive 114 to seal the package. The heat sensitiveadhesive is pre-applied to the cardboard sheet and/or the flat papersheet, and heat is applied from the paper side, conducted to theadhesive via the paper to activate the adhesive. Heat sensitiveadhesives have not been used in the first type of packaging becausecorrugated cardboard sheets are poor heat conductors, and heat appliedto the outer side of the cardboard cannot easily reach the area betweenthe two cardboard sheets where the heat adhesive material would beapplied.

A disadvantage of the second type of conventional packaging is that itsometimes lacks sufficient structural strength. Display packs are oftentransported in an assembly where a plurality of display packs are stoodon their sides in a container with half-height walls (i.e. walls not ashigh as the packs themselves), and wrapped together to form a box-shapedbundle. When two or more of such bundles are stacked on top of eachother, the weight of the top one is supported directly by the packs inthe bottom bundle. The packs therefore must have sufficient structuralstrength and rigidity to prevent them from bending. The lack of physicalstrength also makes it difficult to make larger packages (e.g. largerthan 10 by 15 inches), or to pack heavier items.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a display pack andpackaging method that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

Additional features and advantages of the invention will be set forth inthe descriptions that follow and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention provides a display pack for a product including a first and asecond corrugated cardboard sheet, at least one cardboard sheet definingat least one opening; at least one container having a flat insertionportion and a chamber portion for holding the product, the insertionportion being sandwiched between the two cardboard sheets and thechamber portion protruding from a plane of the cardboard sheets via theopening; and an adhesive material between the first and the secondcardboard sheets in at least a peripheral area of the two cardboardsheets to join the two cardboard sheets together, wherein the first andsecond cardboard sheets are crushed in the peripheral area with reducedair gaps in the corrugations. The adhesive material may be aheat-sensitive adhesive material.

In another aspect, the present invention provides a method of making adisplay pack including the steps of providing a first and a secondcorrugated cardboard sheet, at least one cardboard sheet defining atleast one opening; providing at least one container having a flatinsertion portion and a chamber portion for holding the product; placingthe insertion portion between the two cardboard sheets so that thechamber portion protrudes from a plane of the cardboard sheets via theopening; applying an adhesive material between the first and secondcardboard sheets in a peripheral area of the cardboard sheets; andapplying a pressure to the peripheral area of the two cardboard sheetsto crush the corrugations inside the cardboard sheets in the peripheralarea. The adhesive material may be a heat-sensitive adhesive material,in which case the method further includes applying heat to theheat-sensitive adhesive to activate it.

In another aspect, the present invention provides a device for sealing adisplay pack, which includes an upper and a lower platen, at least oneof the platens having a rim and a recessed central area; and a drivemechanism for driving the platens, the drive mechanism capable ofapplying a force of 25 tons or more at the platens. The platens may beheated.

The present invention provides another device for sealing a displaypack, which includes a transport mechanism for transporting a package;one or more sets of rollers disposed along a path of the transportmechanism, each set of rollers including an upper row and an opposinglower row of rollers, the upper and lower rows of rollers disposed at atapering angle with respect to each other; and a press for applying aforce to at least one of the upper and lower rows of each set ofrollers. The device may include two or four sets of rollers. The rollersmay be heated.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF TUE DRAWINGS

FIG. 1 is a perspective view illustrating a display pack according to anembodiment of the present invention.

FIGS. 2( a) and 2(b) schematically illustrate cross-sectional views ofthe display pack of FIG. 1 along the line 2-2 with platens of a sealingpress.

FIG. 3( a) schematically illustrates parts of a sealing press used toseal a package according to an embodiment of the present invention.

FIG. 3( b) is a schematic plan view of a platen of a sealing pressaccording to another embodiment of the present invention.

FIG. 3( c) is a schematic cross-sectional view of portions of anothersealing press according to another embodiment of the present invention.

FIGS. 4( a) and 4(b) are schematic cross-sectional views showingportions of a sealing press according to another embodiment of thepresent invention.

FIGS. 5( a) and 5(b) are schematic cross-sectional views showing rollersof a sealer machine according to another embodiment of the presentinvention.

FIGS. 5( c) and 5(d) schematically illustrate sealer machines employingrollers according to other embodiments of the present invention.

FIGS. 6( a)-(c) illustrate a package made according to a firstconventional packaging technique.

FIGS. 7( a) and 7(b) illustrate a package made according to a secondconventional packaging technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a display pack according to an embodiment of the presentinvention which has an overall structure similar to that of aconventional packaging shown in FIG. 6( a) but is constructeddifferently. FIGS. 2( a) and 2(b) are cross-sectional views of thedisplay pack of FIG. 1 along the line 2-2 (the differences between FIGS.2( a) and 2(b) will be explained later). As shown in FIGS. 1, 2(a) and2(b), the package 1 is made of two sheets of corrugated cardboard 11 and12 and a plastic container 13 (preferably made of a clear plasticmaterial such as PET) having a flat insertion portion 13 a and a chamberportion 13 b. The insertion portion is sandwiched between the twocardboard sheets 11 and 12, and the chamber portion 13 b protrudes fromthe plane of the cardboard sheets via a cut on one cardboard sheet 11and is used to hold the product inside. Although only one is shown inFIGS. 1, 2(a) and 2(b), a package may contain one or more plasticcontainers, and they may protrude from either or both of the cardboardsheets and may be located are desired positions depending on the productbeing held in the package. Further, a plastic container may be a singlepiece with multiple chambers. The container may be made of a plastic orany other suitable material, and can be of any suitable thickness,color, etc. The front and back sides of the package may be printed withproduct information and other information. The information may beprinted directly on the cardboard, or printed on a litho sheet which isthen laminated onto the cardboard. One to six colors can be printed. InFIGS. 2( a) and 2(b), the corrugations are shown as being parallel tothe vertical direction in FIG. 1, which is preferably the verticaldirection when the display pack is stood on its side when beingdisplayed or transported. Of course, the corrugation can be in otherdirections. The corners of the cardboard sheets may be square, rounded,or a combination of both. The two corrugated cardboard sheets 11 and 12are adhered together at the periphery of the package by a heat-sensitiveadhesive 14 to seal the package. The heat-sensitive adhesive ispreferably pre-applied to the inner sides of one or (preferably) bothcardboard sheets 11 and 12 prior to the sealing operation, but it mayalso be applied during the sealing operation. The adhesive may beapplied to the entire sheet, or a periphery, or any desired areas of thesheet. In one embodiment, the cardboard sheets 11 and 12 are formed ofone cardboard sheet folded over, the cardboard sheet being pre-coatedwith an adhesive on the entire surface.

To seal the package, the peripheral areas 11 a, 12 a of the twooverlaying cardboard sheets are subject to a sufficient amount ofpressure to crush the corrugations inside the cardboard sheets andflatten them in that area. Heat is applied, either simultaneously withor subsequent to the application of pressure, to the outer side ofeither one or both cardboard sheets in the peripheral area. Because thecorrugations inside the cardboard are crushed and the air gaps aresubstantially eliminated, the crushed cardboard becomes a better heatconductor. Sufficient heat can be conducted from the outer side to theinner side where the heat-sensitive adhesive has been applied toactivate the adhesive and seal the package. In one preferred embodiment,the width of the crushed peripheral areas is approximately 0.5 inches.Any suitable sealing width may be used, but it is desirable that theadhesive not be adhered to the insertion portion of the container, sothat the container can be easily removed from the packaging forrecycling. This is desirable because it facilitates recycling of thecontainer. In addition, the container may be made as a re-usablecontainer, and easy removal may facilitate re-use in such a case.

Many types of sealer machines may be used to carry out the sealingprocess, some of which are described below. The first is a sealermachine with a heated sealing press. As shown in FIG. 3( a) (perspectiveview), the sealing press has an upper platen 21 and a lower platen 22.The lower platen 22 is show to have a rim 22 a with a heated surface, arecessed central portion 23 that may accommodate the protrusions 13 b ofthe package being sealed. The upper platen 21 similarly has a heated rim21 a and a recessed central portion (not shown). The rims have a widthdetermined by the desired width of the crushed peripheral areas of thefinished package. Alternative configurations of the sealing press may beused. For example, one of the platens may have a flat surface without arecess, or have a rim wider than the rim of the other platen. If boththe upper and lower platens have rims of similar widths, the crushedperipheral areas of the cardboard sheets may appear depressed on bothsides (see FIG. 2( a)). If one platen is flat or has a rim wider thanthe rim of the other platen, the crushed peripheral areas of thecardboard sheets may appear depressed only on the side of the narrowerrim (see FIG. 2( b)). In the platen configuration of FIG. 2( a), one orboth rim portions 21 a and 22 a may be heated. In the configuration ofFIG. 2( b), preferably only the narrower rim 21 a is heated because itmay be undesirable for areas other than the sealed peripheral areas tobe heated. Heating from both sides may be more desirable as it reducesthe heating time and speeds up the sealing operation.

Preferably, the force or pressure applied by the platens is such thatthe cardboard sheets are crushed to up to approximately 50% of theiroriginal thickness. Generally speaking, within certain limits, higherpressure results in thinner crushed cardboard sheets, which in turnresults in increased heat transfer rate and therefore reduced heatapplication time required to properly activate the adhesive. The optimumpressure may also depend on the type of the cardboard used. Thetemperature of the heated surface may be approximately from 100 to 500degrees F., which is a typical temperature used in the secondconventional packaging technique. Those of ordinary skill in the artwill be able to find acceptable or optimum pressure, temperature andprocess time conditions for the particular cardboard used without undueexperimentation.

In one particular example, the package uses two sheets of 200 lb testE-flute cardboard coated with a heat sensitive blister card coating asan adhesive, has a size of 10 inches by 15 inches and a sealed width of0.5 inches. The sealing press has a rim on both platens and bothsurfaces are heated to a temperature of 300 degrees F. The force on theplatens is 25 tons. The pressure and heat was applied simultaneously for3 seconds.

The sealer machine suitable for the above application may be a machinedused to seal a conventional package of the second type (as shown in FIG.7( a)), modified so that the platens can apply sufficient pressures tocrush the cardboard. The machine has a pneumatically driven upper andlower toggle mechanism to create the pressure. There are four hydraulicunits located under four lower posts which are used as an additionalmeans of raising the press to maximize the pressure. The force on theplatens is adjustable. In one example, the force is approximatelybetween 10 and 75 tons. The upper and lower seal heat is generated withthe use of multiple cartridge heaters controlled through solid staterelays. The temperature of the upper surface is adjustable from 0 to 450degrees F.; the temperature of the lower surface is fixed at 450 degreesF. Additionally, there are chain driven elevators used to move thefixture that holds the packages during assembly and sealing back to theinitial start position.

In addition to the peripheral areas, the corrugated cardboards 11 and 12may be crushed and sealed in certain interior areas (spot sealed) toprovide additional security, especially for larger packages and packageswith multiple separate plastic containers. To achieve spot sealing, asshown in FIG. 3( b) (plan view of a platen), a sealer press is providedwith a number of posts 24 inside the area surrounded by the rim portion21 a and/or 22 a. Opposing posts are provided if both platens have arecessed central portion; alternatively, if one platen is flat, theother platen is provided with the posts 24. The posts are pressured andheated in the same way as the rim portion.

A second type of sealer machine useful for carrying out the sealingprocess is a sealing press similar to the one described above, butinstead of heated platen(s), hot air or a hot steam is applied to theheat-sensitive adhesive to heat it. The hot air or steam is suppliedfrom the side by a tube or pipe 25 as shown in FIG. 3( c)(cross-sectional view). Since a corrugated cardboard typically containsan adhesive to hold its various layers together, it is possible that thehot air or hot steam will melt this adhesive. Thus, after crushing, thelayers of the crushed corrugated board will be adhered together by thisadhesive, resulting in increased structural integrity of the seal. As analternative, heated platen(s) and hot air/hot steam may be used incombination.

FIGS. 4( a) and 4(b) illustrate an alternative embodiment of the sealingpress (either heated or unheated). In this embodiment, the platens aresimilar to those shown in FIGS. 2( a), 2(b), 3(a) and 3(c), but the rimportions 21 a and 22 a have rounded or chamfered edges 21 b and 22 b onthe inside edges, i.e. the edges that correspond to the border betweenthe crushed and uncrushed portions of the package. The rounded shape ofthe edges 21 b and 22 b avoids fanning a sharp line between the crushedand uncrushed portions on the package and avoids potentially tearing orcutting the surface sheet of the cardboard. Desirable radius of therounded edges 21 b and 22 b depends on the thickness of the corrugatedboards, and is preferable about ⅛ to 1 inch. Note that FIGS. 4( a) and4(b) illustrate the stage of the platens before crushing occurs.

A third type of sealer machine according to an embodiment of the presentinvention is shown in FIGS. 5( a)-(d). Instead of a press, parallel setsof rollers are used to seal the package in this type of machine. FIG. 5(a) is a schematic cross sectional view along a side of a package toillustrate the side being sealed by a set of rollers of the sealermachine. The package contains two sheets of corrugated cardboard 11 and12 with an adhesive (not shown) applied between the two sheets in theperipheral areas. The set of rollers of the sealer machine has opposingupper and lower rows of rollers 51 a and 51 b mounted on respectiveroller blocks 52 a and 52 b. The upper and lower rows of rollers 51 aand 51 b are disposed at a tapering angle relative to each other suchthat gap between opposing rollers is slightly greater than the thicknessof two sheets of uncrushed corrugated cardboard at the entrance end (theleft hand side in FIG. 5( a)), and is reduced to the desired thicknessof the two sheets of crushed corrugated cardboard at the exit end. Theangle and the gap are preferably adjustable. FIG. 5( a) shows the lowerrow of rollers 51 b as being horizontal, but other designs are possible;for example, the upper row of rollers 51 a may be horizontal or neitherrow may be horizontal. Alternatively, a front segment of the two rows ofrollers may be disposed at a tapering angle and a back segment thereofare disposed in parallel with a gap equal to the thickness of thecrushed corrugated cardboard sheets. Sufficient pressure is applied tothe roller blocks to crush the corrugations in the cardboard sheets andto seal the package. In one embodiment, the upper roller block 52 a isfixed and the lower roller block 52 b is mounted on a hydraulic presscapable of applying a force of about 0 to 75 tons, preferably about 20to 70 tons. The force is preferably adjustable. One or both rows ofrollers may be heated to a controllable temperature in a similar manneras the temperature control mechanism for the sealing press describedearlier.

Similar to the platens shown in FIGS. 4( a) and 4(b), the rollers 51 aand 51 b may have rounded to chamfered inside edges to avoid potentiallytearing or cutting the surface sheet of the cardboard.

FIG. 5( b) is a schematic top plan view showing a parallel pair ofroller sets 51 a,b (collectively 51) and 53 mounted on a pair of rollerblocks 52 a,b (collectively 52) and 54 as well as a package 1 passingthrough the pair of roller sets. The structures of the roller set 53 andthe roller block 54 are similar to those of the roller set 51 and theroller block 52. The lateral distance between the two roller sets 51 and53 is adjustable to seal packages of different widths. The two rollersets 51 and 53 may be independent rollers; or alternatively, the lowerrows of rollers in the roller sets 51 and 53 may be the same rollersthat extend across the width of the package. In the latter case, onlythe distance between the upper rows of rollers will be adjusted fordifferent package widths.

The pair of roller sets shown in FIG. 5( b) can seal two parallel sidesof a package. To seal the other two parallel sides, the package may bepassed through another, similar sealer machine, or though the same pairof roller sets one more time (after adjusting the distance ifnecessary), or through an additional pair of roller sets of the samesealer machine. FIGS. 5( c) and 5(d) show two preferred sealer machineseach having two pairs of roller sets. In the machine shown in FIG. 5(c), a second pair of roller sets 55, 57 is provided downstream of and atthe same orientation as the first pair of roller sets 51, 53. Thepackage 1 is first transported by a transport mechanism in a firstdirection as indicated by the arrow A and sealed on two sides by thefirst pair of roller sets 51, 53. Then, the package is rotated 90degrees (as indicated by the arrow C) by a rotation mechanism andcontinues to move in the same direction (as indicated by the arrow D).It then passes through the second pair of roller sets 55, 57 (asindicated by the arrow B) and is sealed on the other two sides. In themachine shown in FIG. 5( d), a second pair of roller sets 55, 57 isprovided at a right angle with respect to the first pair of roller sets51, 53. The package 1 is first transported in a first direction (asindicated by the arrow A) and sealed on two sides by the first pair ofroller sets 51, 53, and then, without changing its orientation, istransported in a second direction (as indicated by the arrow B) at aright angle to the first direction. It then passes through the secondpair of roller sets 55, 57 (as indicated by the arrow B) and is sealedon the other two sides. In the machines shown in FIGS. 5( c) and 5(d),the distances between the roller sets 51 and 53, and 55 and 57 in thefirst and second pair of roller sets are adjusted for the two widths ofthe package, respectively. The structures of the transport mechanism,the rotation mechanism and the mechanism for adjusting the distancebetween roller sets are not described in detail here as they are withinthe level of skill of artisans in the mechanical art.

The package in FIG. 1 is shown to be sealed with the adhesive on allfour sides. Alternatively, instead of sealing around the entireperiphery with the heat-sensitive adhesive, the package may be sealed inselected peripheral areas only. In particular, the two cardboard sheets11 and 12 may be made of one board and folded once in the middle, andthe side of the package corresponding to the fold line may not need tobe sealed with the adhesive (although it is preferable to seal it aswell). In such cases, the platens of the sealing press may beconstructed so that heat and pressure are only applied to the areaswhere seals are to be foamed.

The packaging technique according to embodiments of the presentinvention has the following advantages. The packages are more secure andharder to tear from the edge and the center than packages made by thefirst conventional method described above which uses hot melt glue. Thesealing quality is also more consistent than seals using glue becausethe drying (cooling) speed and the placement of the hot melt glue arehard to control. Packages made with the present technique are alsoaesthetically more appealing than packages made by the first and secondconventional techniques in that the corrugations of the cardboard sheetsare less visible when viewed from the side edges (e.g. the bottom side)due to the crushing. Compared to the second conventional packagingtechnique, packaging made with the present method is stronger because ituses two cardboard sheets. As a result, the packages can be made largerand to pack heavier items, and multiple packages can be stacked inbundles. For example, the packages can be as large as 24×24 inches(whereas the second conventional type of packages are typically up to14×14 inches) and can be used to pack items as heavy as 10 to 20 lbs.Also, the second type of conventional packages have a tendency to warpbecause the two sheets are of different materials. Packages according tothe present invention are also more environmentally friendly becauseunlike the cardboard used in the present technique, the flat sheet ofpaper used in the conventional method uses less post-consumer recycledmaterial. The present sealing technique is also faster than the processused in the second conventional technique.

Although the above-described embodiments are most advantageous when usedin combination with a heat-sensitive adhesive, the crushing techniquedescribed above may also be applied when a regular, non-heat-sensitiveadhesive is used. Such a package has the advantages that it is harder toopen and tear from the edge than packages made by the first conventionalmethod described above because the corrugations is crushed in the edgeareas. It is also aesthetically more appealing than packages made by thefirst and second conventional techniques in that the corrugations of thecardboard sheets are less visible when viewed from the side edges due tothe crushing.

It will be apparent to those skilled in the art that variousmodification and variations can be made in the display pack andpackaging method of the present invention without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention cover modifications and variations that come within the scopeof the appended claims and their equivalents.

1. A layered cardboard composite structure comprising: first and secondlayers, the first layer comprising a corrugated cardboard sheet having afirst upper facing, a first lower facing and a first inner corrugatedmember with first corrugations and first air gaps between the firstupper and first lower facings, and the second layer comprising one of asheet of paper or a sheet of corrugated cardboard, the layered compositestructure comprising a peripheral edge, a generally uniform originalthickness, at least one peripheral area extending inwardly from theperipheral edge to an inner boundary, and an inner area wherein the atleast one peripheral area is crushed to a thickness less than theoriginal thickness.
 2. A layered composite structure of claim 1, whereinthe air gaps in the at least one crushed peripheral area aresubstantially eliminated.
 3. A layered composite structure of claim 1,wherein the thickness of the at least one crushed peripheral area is nomore than 50% of the original thickness.
 4. A layered compositestructure of claim 1, wherein the peripheral edge comprises at least onesubstantially straight section and at least a portion of the innerboundary is generally parallel to a straight section of the peripheraledge.
 5. A layered composite structure of claim 1 wherein the distancebetween the at least one substantially straight section and the at leasta portion of the inner boundary is about 0.5 inch.
 6. A layeredcomposite structure of claim 1, further comprising an adhesive betweenthe first and second layers in the at least one peripheral area.
 7. Alayered composite structure of claim 1, wherein the first corrugationsare parallel to a vertical direction when the structure is stood on itsside when being displayed or transported.
 8. A layered compositestructure of claim 1, wherein an outer surface of the at least onecrushed peripheral area has a generally flat depressed area.
 9. Alayered composite structure of claim 8, wherein each of a front outersurface and a back outer surface of the at least one crushed peripheralarea each has a generally flat depressed area.